A series of oxyfluoride chains containing asymmetric basic building units of both early- and late-transition metal cations

Abstract

Four new transition metal oxyfluorides revealing chain structures composed of asymmetric basic building units of [MO2F4]2− (M = Mo and W) and [M’(pz/mpz)4]2+ (M′ = Cu and Ni) polyhedra, i.e., [Cu(mpz)4][MoO2F4] (1), [Cu(pz)4]2[WO2F4]2 (2), [Ni(pz)4]2[MoO2F4]2 (3), and [Ni(pz)4][WO2F4] (4) (pz = pyrazole; mpz = 3-methyl pyrazole) have been synthesized via hydrothermal reactions. The linear chain structures found from the title compounds are attributable to the trans-directing [MO2F4]2- octahedral moiety and hydrogen bonding interactions. Strong Jahn–Teller distortions are observed for Cu2+ cations with d9 configuration in compounds 1 and 2. All the compounds show both lower-energy and higher-energy absorption band gaps, which originate from the d–d transitions and the distortion of octahedral geometry of M2+ cations, respectively. The magnetism of [Cu(mpz)4][MoO2F4] turns out to be described by noninteracting Cu2+ spins rather than a spin chain due to long exchange path mediated via the nonmagnetic Mo6+ ions. The title compounds have been also thoroughly characterized using spectroscopic and thermal analyses along with calculations of local dipole moments and the extent of out-of-center distortions.